Evaluating Gaging For The Shop Floor

Measuring instruments have been used for the inspection of manufactured parts ever since the first vernier caliper was introduced. It wasn't difficult to take care of those old tools on the shop floor: A clean cloth, a little elbow grease and a good storage box were all that was needed to make those gages last a lifetime.

Columns
From:
7/1/2004
Modern Machine Shop,
George
Schuetz

Measuring instruments have been used for the inspection of manufactured parts ever since the first vernier caliper was introduced. It wasn't difficult to take care of those old tools on the shop floor: A clean cloth, a little elbow grease and a good storage box were all that was needed to make those gages last a lifetime. In fact, they often became prized possessions, as craftsmen handed down tools from generation to generation.

In the past 30 years or so, electronic gages have become increasingly common on the shop floor because of their ease of use, speed and ability to do complex measurements. However, when it came to caring for these new gages, one thing was clear: You didn’t want to get that digital caliper, micrometer, indicator, amplifier or computer anywhere near water or coolant, or there was sure to be trouble. Either the gage wouldn’t work, or, even worse, it would produce incorrect readings.

It didn’t make sense that these gages didn’t operate properly in an environment where coolant, grease, dirt and chips were among the normal working conditions.

Recently, there have been improvements in many of the electronic gaging tools that finally give them the characteristics needed to survive on the shop floor. Improvements in scale technology, microcircuits and sealing have made gages capable of literally taking measurements under water.

Now that these types of gages are finally available, a new standard has been created to help identify what type of tool is best for the environment in which it will be used. This rating is called ingress protection (IP). Associated with the IP is a two-digit rating number that tells what type of conditions the gage can survive in. The first digit describes the protection for solid foreign objects, while the second digit indicates protection against harmful ingress of water. A potential third digit, which is the defined impact protection, has not yet made its way into the measuring instrument table (see chart).

For example, a gage might have a rating of IP-65. As you can see from the accompanying table, this gage is totally protected against dust and low pressure jets of water from all directions, with limited ingress permitted. Today there are calipers and micrometers with ratings as high as IP-67. These can be subjected to the type of dust and dirt found in the shop, and they are both coolant proof and waterproof.

So, electronic tools can finally be used on the shop floor. What a good idea! But one cautionary note: Just because these new gages can handle the environment doesn’t mean that their measurements are impervious to environmental conditions. They are still precision gages, and all the basic rules for precision gaging still apply. We’ll review the classic SWIPE paradigm next month.